Various process gases may be used in the manufacturing and processing of micro-electronics. In addition, a variety of chemicals may be used in other environments demanding high purity gases, e.g., critical processes or applications, including without limitation microelectronics applications, wafer cleaning, wafer bonding, photoresist stripping, silicon oxidation, surface passivation, photolithography mask cleaning, atomic layer deposition, chemical vapor deposition, flat panel displays, disinfection of surfaces contaminated with bacteria, viruses and other biological agents, industrial parts cleaning, pharmaceutical manufacturing, production of nano-materials, power generation and control devices, fuel cells, power transmission devices, and other applications in which process control and purity are critical considerations. In those processes and applications, it is necessary to deliver specific amounts of certain process gases under controlled operating conditions, e.g., temperature, pressure, and flow rate.
For a variety of reasons, gas phase delivery of process chemicals is preferred to liquid phase delivery. For applications requiring low mass flow for process chemicals, liquid delivery of process chemicals is not accurate or clean enough. Gaseous delivery would be desired from a standpoint of ease of delivery, accuracy and purity. Gas flow devices are better attuned to precise control than liquid delivery devices. Additionally, micro-electronics applications and other critical processes typically have extensive gas handling systems that make gaseous delivery considerably easier than liquid delivery. One approach is to vaporize the process chemical component directly at or near the point of use. Vaporizing liquids provides a process that leaves heavy contaminants behind, thus purifying the process chemical. However, for safety, handling, stability, and/or purity reasons, many process gases are not amenable to direct vaporization.
There are numerous process gases used in micro-electronics applications and other critical processes or applications. Ozone is a gas that is typically used to clean the surface of semiconductors (e.g., photoresist stripping) and as an oxidizing agent (e.g., forming oxide or hydroxide layers). One advantage of using ozone gas in micro-electronics applications and other critical processes, as opposed to prior liquid-based approaches, is that gases are able to access high aspect ratio features on a surface. For example, according to the International Technology Roadmap for Semiconductors (ITRS), current semiconductor processes should be compatible with a half-pitch as small as 20-22 nm. The next technology node for semiconductors is expected to have a half-pitch of 10 nm, and the ITRS calls for <7 nm half-pitch in the near future. At these dimensions, liquid-based chemical processing is not feasible, because the surface tension of the process liquid prevents it from accessing the bottom of deep holes or channels and the corners of high aspect ratio features. Therefore, ozone gas has been used in some instances to overcome certain limitations of liquid-based processes, because gases do not suffer from the same surface tension limitations. Plasma-based processes have also been employed to overcome certain limitations of liquid-based processes. However, ozone- and plasma-based processes present their own set of limitations, including, inter alia, cost of operation, insufficient process controls, undesired side reactions, and inefficient cleaning.
Other problems relate to the temperature necessary for successful deposition. With respect to silicon nitride (SiN) for example, ammonia (NH3) is currently often used at temperatures in excess of 500° C. or even 600° C. It is expensive to maintain such high temperatures for deposition and it would be preferable to deposit at lower temperatures. In addition, new semiconductor device technologies have stringent thermal budgets, which inhibit the use of elevated temperatures over 400° C. Hydrazine (N2H4) presents an opportunity to explore lower temperatures in part because of the favorable thermodynamics of hydrazine resulting in lower deposition temperatures and a spontaneous reaction to form nitrides. Although reported in the literature (Burton et al. J. Electrochem. Soc., 155(7) D508-D516 (2008)), hydrazine usage has not been adopted commercially due to the serious safety concerns with using hydrazine. Substituted hydrazines, which are generally safer than hydrazine, suffer from the drawback of leading to unwanted carbon contamination. Thus, there is a need to develop a safer method for using hydrazine for either deposition processes or for delivery to other critical process applications.
The gas phase use of hydrazine has been limited by safety, handling, and purity concerns. Hydrazine has been used for rocket fuel and can be very explosive. Anhydrous hydrazine has a low flash point of about 37° C. Semiconductor industry protocol for safe handling of this material is very limited. Therefore, a technique is needed to overcome these limitations and, specifically, to provide substantially water-free gaseous hydrazine suitable for use in micro-electronics and other critical process applications.
Similarly, as explained in PCT Publication No. 2014014511 by Rasirc, Inc., which is hereby incorporated by reference herein, the gas phase use of hydrogen peroxide in critical process applications has been of limited utility, because highly concentrated hydrogen peroxide solutions present serious safety and handling concerns and obtaining high concentrations of hydrogen peroxide in the gas phase has not been possible using existing technology.